Major Depressive Disorder (MDD) is a disabling and particularly persistent mental disorder that is considered to be a priority public health problem. The active human dopamine transporter (DAT), which is encoded by the SLC6A3 gene, regulates the dopamine concentration in the synaptic cleft. In this sense, this neurotransmitter is primordial in modulating human emotions. This systematic review aims to verify the SLC6A3 (DAT1) 3′UTR VNTR (rs28363170) gene variant’s SS (9R/9R) genotype and S (9R) allele frequency fluctuation and its influence on the modulation of pharmacotherapy in MDD. For this purpose, we searched different databases, and after applying the eligibility criteria, six articles were selected. Studies have shown an association between the SS (9R/9R) genotypic and S (9R) allelic presence with the risk of developing MDD, in addition to influencing the decrease in response to antidepressant therapy. However, despite the findings, disagreements were observed between other studies. For this reason, further studies with the SLC6A3 3′UTR VNTR (rs28363170) variant in different populations are necessary to understand this polymorphism’s role in the onset of this disease.

Major Depressive Disorder (MDD) is a highly prevalent multifactorial psychopathology affected by neurotransmitter levels. Monoamine Oxidase A (MAOA) influences several neural pathways by modulating these levels. This systematic review (per PRISMA protocol and PECOS strategy) endeavors to understand the MAOA uVNTR polymorphism influence on MDD and evaluate its 3R/3R and 3R* genotypic frequencies fluctuation in MDD patients from different populations. We searched the Web of Science, PubMed, Virtual Health Library, and EMBASE databases for eligible original articles that brought data on genotypic frequencies related to the MAOA uVNTR variant in patients with MDD. We excluded studies with incomplete data (including statistical data), reviews, meta-analyses, and abstracts. Initially, we found 43 articles. After removing duplicates and applying the inclusion/exclusion criteria, seven articles remained. The population samples studied were predominantly Asians, with high 3R and 4R allele frequencies. Notably, we observed higher 3R/3R (female) and 3R* (male) genotype frequencies in the healthy control groups and higher 4R/4R (female) and 4R* (male) genotype frequencies in the MDD groups in the majority of different populations. Despite some similarities in the articles analyzed, there is still no consensus on the MAOA uVNTR variant’s role in MDD pathogenesis.

Background: Major depressive disorder (MDD) is a disease that has been increasingly affecting more people worldwide. The dopamine D2 receptor (DRD2), encoded by the DRD2 gene, plays critical roles in the brain, one of which is related to reward processes. Aims: The following systematic review aims to analyze the DRD2/ANKK1 TaqIA (rs1800497) polymorphism’s A1 genotype frequency fluctuation in MDD patients and determine its influence on MDD. Methods: Four databases were searched, and the consequent articles were analyzed following the inclusion criteria per the PECOS strategy, resulting in five selected articles. Results: Interestingly, although two articles showed that the A1 allele presence significantly increases the risk of MDD manifestation, most articles did not find a significant association between this DRD2 gene variant and MDD. Conclusions: Most of the included studies were dated, indicating the need for more studies to address the results’ non-conformity with different populations.